1. Field of the Invention
The present invention relates to an AC adapter in which a rotatable insulative plug laterally protrudes and electrically conductive blades to be connected with the AC power source are partly molded in the plug, and more particularly to an AC adapter in which such blades are pivotally supported so as to be rotatable by 90.degree. between a state where the blades are housed in a part of a casing and another state where the blades protrude from the casing.
2. Description of the Related Art
In some of AC adapters, circuit components for converting an AC power source to a DC power source are housed in a casing. Electrically conductive blades for connected to the AC power source are molded in an electrically insulative plug, and the blades are pivotally supported so as to be rotatable by 90.degree. between a state where the blades are housed in a part of the casing and another state where the blades protrude from the casing. Such an AC adapter can be carried with setting the blades into a housed state, and hence is useful in travel or the like.
FIG. 4 is a front view schematically showing the configuration of a usual AC adapter of this type, in a partially transparent manner. In the figure, 10 denotes an insulative resin casing, 20 denotes a pair of blades which are made of an electrically conductive metal material, and 30 denotes an insulative resin plug which is formed by partly molding the blades 20. In the casing 10, a printed circuit board is housed on which circuit components for converting an AC power source to a DC power source are mounted. The board is not shown in the figure. The plug 30 has a rotation shaft 31 which protrudes from one face of the plug. A bearing structure for supporting the rotation shaft 31 is formed in the casing 10. Since the blades 20 are integrated with the plug 30, the blades can be rotated by 90.degree. about the shaft 31 between a state (indicated by broken lines) where the blades are housed in a part of the casing 10 and another state (indicated by solid lines) where the blades protrude from the casing 10.
FIGS. 3(A), 3(B), and 3(C) are a front view, a side view, and a plan view which show the related structure of the blades 20 and the plug 30, respectively. The plug 30 has an end face 32 from which terminal portions 21 of the blades 20 to be connected with the AC power source protrude, and first and second faces 33 and 34 which are perpendicular to the end face 32 and opposed to each other. The rotation shaft 31 protrudes from the first face 33 in a direction perpendicular to the blades 20. Contact portions of the blades 20 are exposed from the second face 34 without protruding therefrom.
Contactors 40 which are to be respectively elastically contacted with the contact portions 22 of the blades 20 as shown in FIG. 3(B) are disposed on the printed circuit board in the casing 10. The contactors 40 are contacted with the contact portions 22, only under a state where the blades 20 protrude from the casing. FIG. 3(C) shows a state where the blades 20 are housed in the casing 10. Under this state, the contact portions 22 of the blades 20 are located at positions which are rotated by 90.degree. from the respective contactors 40, or separated from the contactors 40.
In the structure shown in FIG. 3, the contact surfaces of the contact portions 22 of the blades 20 are in the same plane as the second face 34 of the plug 30, so that the contactors 40 on the side of the casing are always pressingly contacted with the contact portions 22 of the blades 20 or the second face 34 of the plug 30. When the blades 20 are repeatedly rotated, therefore, the second face 34 of the plug 30 wears and shavings are produced. Since the shavings are electrically insulative, interposition of the shavings between the contactors 40 and the contact portions 22 causes a contact failure. This is a first problem which is to be solved by the invention.
In the structure of FIG. 3, furthermore, a clearance gap 11 inevitably exists between the casing 10 and the plug 30 as shown in FIG. 3(C). Therefore, there is a possibility that a foreign matter enters the interior of the casing 10 through the gap 11. When the foreign matter is electrically conductive, it causes an electric circuit in the casing 10 to be short-circuited. This is a second problem which is to be solved by the invention.